1. Field of the Invention:
This invention relates generally to ladders capable of supporting a single human, and more specifically to a folding step ladder capable of being extended incrementally to a variety of heights.
2 . Description of the Related Arts:
Ladders that are capable of supporting a single person have in the past generally fallen into one of two broad categories commonly referred to as "step" ladders and "straight" ladders. Step ladders are characterized by their ability to be self supporting, which is in contrast to the requirement that straight ladders have an external support of some type. The external support for a straight ladder is generally provided for by leaning the ladder against a stable vertical structure. Straight ladders are frequently constructed as "extension" ladders of some form that are capable of adjusting to a variety of lengths depending upon the needs of the user. Step ladders are utilized more frequently in the interior of buildings or other structures where heights have upper limitations determined by the ceiling or roof of the structure. By contrast, straight and extension ladders are more frequently employed on the exterior of structures, or on exterior objects such as trees, fences, etc.
It is clearly advantageous to be able to rely on the self supporting features of a ladder if possible. The problem is that self support generally means adding additional components to the ladder. These supplemental components add bulk, weight, etc., that all contribute to the problems of handling and moving the ladder. On the other hand relying on the availability of an external support for a straight or extension ladder might be equally impractical.
Neither type of ladder can fulfill all the functions of the other type, and so both are commonly utilized and both may be required at any particular job site.
Given that it is an advantage to have some form of self support, it is also very clear that at some point, with a continuous increase in ladder height, the above mentioned problems outweigh the advantages of self support. Within certain height requirements, however, there is no doubt that the self support and stability of a step ladder make it the more practical choice over a straight ladder of comparable height.
Straight ladders have one general advantage over step ladders in that they more easily incorporate extendable components. While the same factors that demand extendable straight ladders would also demand extendable step ladders, the mechanics of creating extendable step ladders has always been more complex than that for straight ladders.
Step ladders are most frequently used in indoor situations and are constructed in standard heights that range from two feet to ten feet. There are larger step ladders being manufactured but after about ten feet in height the lateral stability of the ladder diminishes. The most common heights are six, eight, and ten foot ladders.
Because an extendable step ladder is inherently more complex than an extendable straight ladder the industry's solution has been to simply provide more than one size of ladder. While this may indeed simplify the structure of any individual ladder it creates a number of new problems. It is not unusual for those who frequently use step ladders to maintain a variety of different ladders of varying heights for just such different applications. The necessity of purchasing and transporting a plurality of different step ladders to meet the requirements of various applications often proves costly and cumbersome.
An unfortunate by-product of the necessity of having a variety of step ladder sizes results when users are reluctant to switch ladders when a taller height is required. More often then not the worker faced with a momentary task at a greater height will attempt to reach that height by standing on the top hinge step of the ladder. Needless to say this is potentially very dangerous. Were it easier to provide the ladder height needed workers would be less inclined to "stretch" the reach capabilities of an otherwise appropriate step ladder.
It would be advantageous to combine the self support and stability of the step ladder with the extendibility found in many straight ladders. If a single step ladder could fulfill the function of a six foot ladder and an eight foot ladder, and not have the cost or the bulk of two separate ladders, then many of the above described problems could be solved.
There are extendable step ladders designs that are known and have been employed in the past. These designs, however, all suffer from high cost and complexity. Some of these designs try to do too much, i.e. try to provide heights variable over too great a range. Some of these are overly complex, and thus costly, because they attempt to provide an infinitely variable height rather than an incrementally variable height. Still other designs obtain suitable results only at the expense of great additional bulk and weight.